In the 3GPP (3rd Generation Partnership Project), in order to reduce operation expense (OPEX) incurred in a drive-test by an operator, utilization of a radio terminal for measurement and report of such information that has been collected by the drive-test or information similar thereto is under study (Non Patent Literature 1). An ultimate object of the above-mentioned study is the minimization of execution of the drive-tests, and the technology related to this study is collectively called “MDT” (Minimization of Drive-Tests). An application target of the MDT is both UMTS (Universal Mobile Telecommunication System) and LTE (Long Term Evolution), which are cellular systems defined in 3GPP. The term “measurement” herein also includes “detecting” a certain specific situation.
In MDT, the following two methods are defined as a method for obtaining (that is, measurement and logging of the measurement results) and reporting measurement information by a radio terminal (Non Patent Literature 1).
1. Immediate MDT: The method that instructs a radio terminal to obtain and report measurement information in an active state; and
2. Logged MDT: The method that instructs a radio terminal to obtain measurement information in an idle state, and report the obtained measurement information in an active state.
In the study of MDT, making a determination which radio terminal is instructed to obtain and report measurement information in the network side, that is, control of obtaining and reporting measurement information through a radio terminal initiated by the network is a basic principle, and the following two methods are defined in Non Patent Literature 2.
A. Management based method (Management based MDT): The method that first defines an area to be a target for collection of measurement information in MDT, and then select one arbitrarily from radio terminals that stay in the area. It is also called as Area based method (Area based MDT).
B. Signaling based method (Signaling based MDT): The method that selects a specific radio terminal based on a individual ID (Identity) of the radio terminal.
Next, there will be described a logged MDT using a management based method in LTE studied in 3GPP with reference to FIG. 1. As shown in FIG. 1, a system of LIE assumed herein includes a radio terminal UE (User Equipment), a radio base station eNB (evolved NodeB), an network apparatus EPC (Evolved Packet Core) including such as a mobility management apparatus MME (Mobility Management Entity)/a home subscriber management server HSS (Home Subscriber Server) of a radio terminal, a network operation management apparatus EM (Element Manager) (also called as EMS: Element Management System), and trace information collecting apparatus (Trace Collection Entity). Then, in FIG. 1, the logged MDT using the management based method is executed in the following steps. Note that in FIG. 1, the UE is assumed to be in a RRC (Radio Resource Control)_Connected state (active mode) at the start of step S1001.
Step S1001: The UE notifies a connected eNB of terminal capability information (UE Capability Information) on radio access. At this time, support of the logged MDT (logged Measurements Idle) is notified together.
Step S1002: The EM(S) requests the eNB to execute the logged MDT on a management basis (Trace Activation Request). The instruction also includes configuration information necessary for executing the logged MDT.
Step S1003: The eNB selects the UE that is instructed to execute the logged MDT according to the request from the EM(s) as well as terminal capability information of the UE (UE selection). Although not shown in the figure, the eNB obtains in advance consent information (user consent) related to the detailed location information of the UE (e.g. GPS location information) from (MME that is included in) EPC. When necessary to report the detailed location information, the eNB may select a consent UE, and when not necessary, the eNB may select an unconsent UE.
Step S1004: The eNB notifies the UE of configuration information necessary for executing the logged MDT (Logged Measurement Configuration). This notification is also an instruction to execute the logged MDT.
Step S1005: The eNB changes the UE to a RRC_Idle state (idle mode) (RRC Connection Release).
Step S1006: The UE changes to a RRC_Idle state (RRC Connection Release).
Step S1007: The UE performs measurement for signals in the serving cell or neighboring cells at a predetermined timing. Herein, the measurement items may include received power (Reference Signal Received Power: RSRP) or received quality (Reference Signal Received Quality: RSRQ) of a known signal (Reference Signal: RS). Note that the measurement is performed for cell reselection or the like, but not for the logged MDT which is additional.
Step S1008: The UE logs the measurement results (RSRP or RSRQ) at a logging timing indicated by configuration information of the logged MDT. Note that in the specification, a combination of operations in steps S1007 and S1008 (or what includes at least these two operations) is called “logging of measurement results” (Log measurement results) for the sake of simplification, unless specifically described
Step S1009: The UE performs a RRC connection request to become a RRC_Connected state in response to a predetermined trigger.
Step S1010: The eNB accepts the RRC connection request and notifies necessary information (RRC Connection Setup).
Step S1011: The UE transmits a confirmation message for RRC connection establishment (RRC Connection Setup Complete). In a series of operations from step S1009 to S1011, a RRC connection is established (RRC Connection Establishment). Herein, the UE that stores record of measurement results (log) transmits a message with the addition of information indicating storing the log (LogMeasAvailable) in the logged MDT.
Step S1012: The eNB requests a log report when notified of storing the log (UE Information Request (LogMeasReportReq)).
Step S1013: The UE reports a log in response to a request of the log report (UE Information Response (LogMeasReport)).
Step S1014: The eNB transfers the reported log to the TCE (Trace Recording Report).
The logged MDT on a management base method is realized through the above-described operations.
In the logged MDT, even when the UE moves from a cell having received configuration information of the logged MDT (that is, requested to execute the logged MDT) to a different cell, it is continued when a destination cell satisfies the predetermined conditions. The predetermined conditions herein are such as a cell that has the same Radio Access Technology (RAT) as the cell having received configuration information of the logged MDT, a cell that belongs to the same PLMN Id (Public Land Mobile Network) as the cell having received configuration information of the logged MDT, or a cell that belongs to a global cell Id (EUT RAN Cell Global Identifier: ECGI) and a tracking area (TA), both of which are indicated by the configuration information.
On the other hand, when a destination cell does not satisfy the predetermined conditions, for example, when moving to a cell of the different RAT, that is, a cell of the different type of system as shown in FIG. 2 (S1105: Cell reselection to UMTS cell), UE stops the logged MDT (S1106: Stop logging measurement results). At this time, the UE does not report a log even when being in a RRC_Connected state (S1109: RRC Connection Setup Complete) for update of location registration in the cell or the like (S1110: Location Update). Meanwhile, the UE restarts the logged MDT when moving again to a cell that satisfies the predetermined conditions. Note that when the UE newly receives configuration information of the logged MDT after moving to a cell that does not satisfy the predetermined conditions (that is, requested to execute the logged MDT), the stored configuration information of the logged MDT or the stored log is overwritten (or discarded).